1. Field of the Invention
The presents application relates to a semiconductor device, in particular, the present application relates to a nitride semiconductor device formed on a semi-insulating silicon carbide (SiC) substrate.
2. Background Arts
A nitride semiconductor device, for instance, a field effect transistor (FET) such as high electron mobility transistor (HEMT) has been installed in a base station of the mobile communication system as an elementary device 15 showing high power at higher frequencies. A Japanese Patent laid open No. 2006-286741A has disclosed a HEMT device stacking, on a semi-insulating SiC substrate, semiconductor layers of an aluminum nitride (AlN) buffer layer, a gallium nitride (GaN) channel layer, and aluminum-gallium nitride 20 (AlGaN) carrier supplying layer in this order.
The gradual decrease of the drain current under a constant bias condition, which is often called as the current collapsing, may be suppressed by adequately setting a thickness of AlN buffer layer. However, the current reduction in a short time after the shut-off of the input high frequency signal, which is often called as the instantaneous current reduction, has been left as a subject to be solved.